Mercruiser 5.7L dual temp sensors?

I have a '97 Larson Escape that I have owned since new. The temp guage stopped working and the guage had lots of moisture in it so i replaced it. It still doesn't work, so I tried to find the sensor and check it out but it appears there are 2 sensors in the water jacket very close to eachother. I was hoping they worked like a typical car guage in that I could ground the wire to the block and ther guage would go full scale. Well, neither of the wires to ground made any change in the guage reading. The guage always stays at the Cold end of the guage. I do have a good ground and 12V at the meter.

I then tried to trace the wire from the guage back to the engine compartment, but I can't find it, either visually or with an ohm meter.

The ohm meter shows one of the 2 sensors is around 400 ohms (cold) but the other sensor shows open (meg ohms).

Can anyone point me to a wiring diagram / picture so I can figure which sensor is supposed to run the temp guage so I can continue to troubleshoot it.

Thanks

Pete

 

The 400 ohm sensor is for the temp gauge, the other one is a normally open switch, which closes when the water temp is above a threshold (almost boiling) and sounds an alarm. It is wired in parallel with a similar oil pressure switch which closes when there is no pressure.

You may not have the audible alarm installed in your boat because Mercruiser wants to be paid extra for that feature, but the engine always has the sensors installed for it.

 

Thanks CDK. Actually I do have the alarm I guess. When I switched the wires between sensors, the alarm went off.

So the 400 Ohm sensor wire should go directly to the S terminal on the guage I assume. I'll have to track it down and see where the open is.

Thanks for your help.